Radiation-emitting devices are used for the treatment of cancerous tumors within patients. The primary goal of treating cancerous tumors with radiation therapy is the eradication of the cancerous cells, while the secondary goal is to avoid, to the maximum possible extent, damaging healthy tissue and organs in the vicinity of the tumor. Typically, a radiation therapy device includes a gantry that can be rotated around a horizontal axis of rotation during the delivery of a therapeutic treatment. A particle linear accelerator (“LINAC”) is located within the gantry, and generates a high-energy radiation beam of therapy, such as an electron beam or photon (x-ray) beam. The patient is placed on a treatment table located at the isocenter of the gantry, and the radiation beam is directed towards the tumor or lesion to be treated.
Radiation therapy typically involves a planning stage and a treatment stage. In the planning stage, an X-ray computed tomography (CT) scanner (or similar device) is used to acquire images of a lesion. These images are used to accurately measure the location, size, contour, and number of lesions to be treated in order to establish a dose distribution, and various other irradiation parameters in an attempt to irradiate the lesion while minimizing damage to surrounding healthy tissue.
The advent of 3D conformal radiation therapy (3DCRT) and intensity modulated radiation therapy (IMRT) has improved the ability to minimize this damage. 3DCRT and IMRT use multiple, intersecting, shaped radiation beams, each of which geometrically conforms to the shape of a tumor from the view point of the origin of the radiation beam (the “beam's eye view,” or “BEV”). Various types of devices are used to conform the shape of the radiation treatment beam to encompass the tumor along the radiation treatment BEV as it traverses the patient's body into the tumor. One such beam-shielding device is the multi-leaf collimator (“MLC”).
LINACs with MLCs facilitate delivery to a patient of radiation beams with arbitrary shapes and distributions. The MLC patterns can be defined during planning, and coupled with 3D conformal treatment planning techniques, they allow treatment plans to be more flexible and complex. Such MLC-based 3DCRT plans prescribe radiation field geometries tailored to fit the tumor's shape more accurately than previous, 2D block-shaped plans. As a result, higher doses can be targeted at the tumor, requiring tighter safety margins around the tumor to avoid damaging healthy tissue by exposing it to the higher, deadlier doses.
Miniature multi-leaf collimators (MMLCs) are also used for finer confirmation of radiation beams. The leaf widths for a miniature multi-leaf collimator are typically thinner than those for a multi-leaf collimator, usually in the range of 2-4 mm. Conventionally, miniature multi-leaf collimators are mounted onto the head of the LINAC just prior to administration of radiotherapy that requires finer confirmation, such as stereotactic radiosurgery or conformal stereotactic radiotherapy. When the treatment is completed, the miniature multi-leaf collimator is then removed from the linear accelerator.
The procedure of mounting and de-mounting a miniature multi-leaf collimator from a LINAC requires additional time and quality assurance checks, and may risk injury to the patient lying on the treatment couch. Further, it may be difficult to use such a collimator to deliver treatments which use combined fields such as miniature multi-leaf conformed fields and larger fields which are shaped by a larger multi-leaf collimator or other radiation shaping devices such as cut blocks, wedges, radiation jaws, and similar devices. In addition, in some clinical applications it is desirable in the treatment of a specific patient at a particular radiation beam angle to use a narrow conformal field, as would be provided by a miniature multi-leaf collimator, and subsequently use a broader field, as would be provided by a multi-leaf collimator.